1. Field of the Invention
The present invention relates to a pressure sensor for use in such as hydraulic control and measurement of intake pressure and exhaust pressure in automobiles and a method of manufacturing the same. More particularly, the present invention concerns a diaphragm for a pressure sensor using a semiconductor which excels in processing accuracy and can be made ultra-compact and a method of manufacturing a diaphragm for a pressure sensor in which the diaphragm thickness is uniform and the yield is excellent.
2. Description of the Related Art
Semiconductor pressure sensors are used in a wide range of fields since they are compact and excellent in accuracy. Conventional diaphragms for pressure sensors are formed by subjecting silicon substrates to chemical etching, e.g., electrochemical etching. In the case of a compact pressure sensor using a diaphragm formed of a silicon single crystal, a silicon single-crystal substrate is etched by setting {110} faces as crystal faces and a &lt;211&gt; direction as the longitudinal direction of the diaphragm so as to form the diaphragm. However, the operating efficiency involved in manufacturing this pressure sensor has been poor since the measurement of the thickness of the diaphragm and etching are repeated a number of times in order to improve the accuracy of the diaphragm thickness.
FIG. 3 is a schematic cross-sectional view illustrating a conventional pressure sensor.
The crystal faces of a silicon substrate 32 are set at {110} faces. A cavity 34 is formed in the silicon substrate 32 by means of etching, and a diaphragm 36 of a silicon single crystal is thereby obtained. The etching process is controlled in such a manner that those side walls of the cavity 34 that are respectively arranged along the longitudinal direction of the diaphragm 36 constitute {111} faces. However, since etching and the measurement of the diaphragm thickness are repeated to control the thickness of the diaphragm 36, the operation is complicated, and the yield of wafers has been poor due to the roughness of the etched surface of the diaphragm 36. Furthermore, it has been difficult to improve the processing accuracy of the diaphragm thickness owing to variations in the uniformity of the thickness of the silicon wafer prior to processing as well as during etching.